1) Preheat the oven to 220°C/gas mark 8.
2) Arrange the tomatoes on a sheet pan, cut side up, in a single layer. Drizzle with the olive oil and balsamic vinegar. Sprinkle the garlic, sugar, salt and pepper over the tomatoes. Roast for 25 to 30 minutes, until the tomatoes are concentrated and beginning to caramelise.
Serve warm or at room temperature.